This application claims priority under U.S.C. §119(a) on Patent Application 2005-214621 filed in Japan on Jul. 25, 2005, the entire contents of which are herein incorporated by reference.
The present invention relates to photoelectric encoders for detecting code strips, and electric devices provided with such photoelectric encoders.
Conventionally, for example as disclosed in JP 2004-506884A, there has been technology in which a code wheel is inserted between a light-emitting element and a light-receiving element that are in opposition and is rotated, and this code wheel is detected. Here, although particular attention is placed on the lens shape and the lens material etc. of the light-emitting element, the structure is such that the code wheel easily comes into contact with the light-emitting element, the light-receiving element and the lens, and no special measures are taken to avoid this contact. Thus, the light-emitting element, the light-receiving element and the lens etc. become soiled, and this lowers the precision with which the code wheel is detected.
JP H10-235958A discloses a magnetic encoder that detects the magnetic state of a scale portion that is magnetized. In this case, although the detection precision does not drop if the scale portion or the detection portion, for example, becomes soiled, the magnetic encoder has a complex structure and this increases costs.
Further, JP 2004-160871A discloses an optical encoder that optically reads a scale. Here, cleaning members are provided on either side of the scale, and when soiling has been detected by a soils detection sensor, the encoder sensor is moved to and cleaned by the cleaning members. However, the structure is complicated by the fact that it is necessary to provide a soils detection sensor and cleaning members, for example. When the cleaning ability of the cleaning members worsens, there is a drop in the precision with which the scale is detected. Additionally, like in JP 2004-506884A, the structure is such that the scale easily comes into contact with the light-emitting element, the light-receiving element or the lens, for example, and no particular steps have been taken to avoid this contact.
In this way, the structure of conventional optical encoders is such that the code wheel or the scale etc. easily comes into contact with the light-emitting element and the light-receiving element and the lens, for example, and no specific steps are taken to avoid this contact, and thus the light-emitting element, the light-receiving element and the lens, for example, will become soiled and this lowers the precision with which the code wheel or the scale etc. is detected.
The photoelectric encoders generally used in printers, for example, are provided with a recessed groove between the light-emitting element and the light-receiving element, and a code strip (this corresponds to a code wheel or scale) is passed through this groove. In one example, the width of the recessed groove is set to about 0.5 mm and a 0.19-mm thick code strip is passed there through. Therefore, it could be said that there is a clearance of 0.31 mm around the code strip. Thus, there was a wide gap around the code strip from which ink, for example, could enter the recessed groove and soil the light-emitting element and the light-receiving element.